The present invention relates to a process for the preparation of perpropionic acid from hydrogen peroxide and propionic acid.
The synthesis of perpropionic acid from hydrogen peroxide and propionic acid is known (Swern, Organic Peroxides I, Wiley 1970, page 369-372). The reaction of hydrogen peroxide with propionic acid takes place in the presence of an acid catalyst according to equation (1) ##STR1## to give an equilibrium mixture which contains perpropionic acid, propionic acid, hydrogen peroxide, water and the acid catalyst. The concentration of perpropionic acid depends on the concentration of the feed materials and the molar feed ratio of hydrogen peroxide and propionic acid. In general, hydrogen peroxide is used in concentrations of 30 to 90% by weight, preferably 50 to 70% by weight. Propionic acid is preferably employed in the pure form or as an aqueous solution.
Suitable acid catalysts are the mineral acids, for example sulphuric acid, acid salts, such as, for example, sodium bisulphate, or cation exchangers based on sulphonated, partially crosslinked polystyrenes in the H+ ion form. The amount of these catalysts can vary within wide limits.
The mixtures formed according to the equation (1) can be used in a known manner for oxidation reactions.
The equilibrium mixtures formed according to equation (1) also arise as intermediates in processes for the preparation of anhydrous perpropionic acid solutions (DT-OS (German Published Specification No.) 2,262,970).
It is therefore extremely important to be able to prepare and handle the said reaction mixtures under explosion-proof conditions.